The present invention relates to a multilayer film which is heat sealable over a broad temperature range. It is desirable to have a broad sealing temperature range to increase the production of packaging machines. The present invention also relates to a multilayer film which provides easy opening and hermetic seals to packages.
Packaging technology has over the years required the development of many disciplines. Currently packaging technologists integrate elements of engineering, chemistry, food science, metallurgy, and other technologies in order to provide the consumer fresh, healthy dry or liquid. food product. In those cases where packages are prepared from multilayer film, it is desirable to be able to provide a hermetic seal, i.e., a seal which does not permit passage of gas, such as air.
Oriented polypropylene films with thin sealable surface layers of ethylene-propylene copolymers or ethylene-propylene-butene-1 terpolymers have been used in packaging operations. However, these films have not yielded hermetic seals on bags made with the films on packaging machines operated at standard conditions. Hermetic seals are required when leak free packaging is important.
Additionally it is also desirable to provide seals which can be readily opened by the consumer without creating a `z-direction` tear. A z-direction tear is one which cause the disruption of the integrity of the multilayer film when the film is pulled apart at the seal. A z-direction tear is one which does not simply separate at the line at which the seal is formed. Instead, the separation extends to layers of the film when ripped along the layers thereof and not simply delaminated one from another. As a result of z-direction tears, it is difficult to reclose such packages to maintain freshness of the contents. When z-direction tears can be eliminated, packages are easily refolded and sealed by a mechanical means such as a clip
Accordingly it is the object of the present invention to provide a film which yields hermetic seals over a broad temperature range and provides easy opening on bags.
It is a further object of the present invention to provide easy opening with directional tear.
It is still a further object to provide re-sealable packaging with a zipper attachment.